The primary objective of these studies is to examine the effects of limited exposure to chemopreventive agents on both palpable tumor lesions as well as "normal at risk" breast tissue. Studies being performed: 1) Palpable tumors (at least 6) from control MNU treated rats as well as palpable tumors from rats treated with at least 10 different chemopreventive regimens (this would consist of 6 different chemicals with at least four of the agents being examined at two different doses). Differential expression studies are employing a limited number of genes ( 100 which they have previously shown demonstrate altered expression in the MNU tumor model as compared to normal rat epithelia or genes which have been demonstrated to show altered expression in human mammary tumors. Also studied are 1) Pooled normal rat mammary gland from control MNU treated rats as well as pooled normal rat mammary glands treated with at least 10 different chemopreventive regimens (this would consist of 6 different chemicals with at least four of the agents being examined at two different doses). Candidate genes include data from CGAP, published papers and any data which they themselves have defined relative to human breast cancer. Candidate chemicals include: 1) An aromatase inhibitor 2) An antiangiogenic agent 3) A retinoid 4) A farnesyltransferase inhibitor. Stuidies include comparative levels of expression of various genes in pooled control (untreated or vehicle treated ) mammary glands as contrasted with mammary glands from rats treated with various chemopreventives for 4 or 10 days. These studies are also examining the effects of limited exposure to chemopreventive agents on both small palpable lung lesions as well as normal lung tissue.